Structure for reduction of audible sound



T Jan. 17, 1956 H. c. STEWART ET AL STRUCTURE FOR REDUCTION OF AUDIBLE SOUND Filed July 26 1951 Fig.1.

Inventors: Harroid Q. StQWaT-t, James E. Hocomb Their" Attdrneg.

United States Patent I O STRUCTURE FOR REDUCTION OF AUDIBLE SOUND Harold C. Stewart, Pittsfield, and James E. Holcomb,

Lanesboro, Mass., assignors to Generai Electric Company, a corporation of New York Application July 26, 1951, Serial No. 238,757

1 Claim. 01. 336-65) This invention relates to structural means for reducing audible sound transmitted by enclosure-contained sound propagating devices and more particularly to structural means for reducing audible sound transmitted by tankenclosed electrical apparatus.

Certain types of electrical apparatus which produce an audible sound are contained within metallic enclosures, and are normally rigidly connected to such enclosures by means of metallic connecting members. When such an electrical apparatus produces an audible sound, the members connecting the apparatus to the enclosing means serve as conductors of the audible sound produced by the apparatus, and conduct such audible sound to the surface of the enclosure means and thence, to' the exterior of the enclosure means. For example, the magnetic core of a transformer is an oscillator or source of sound in the transformer. Sound is propagated from this source to the exterior of the transformer casing through the metallic members which connect the transformer core to the enclosing tank. Also, where the electrical apparatus is immersed in an insulating liquid, the liquid acts as a sound conductor. Interference with the propagation of sound waves through the structural connecting members or through the liquid insulating medium will reduce the sound which is transmitted to the exterior of the transformer casing.

Accordingly, it is an object of our invention to provide a new and improved means for isolating the sound produced by a sound propagating device.

It is a further object of this invention to provide a new and improved sound isolating device for electrical apparatus contained Within an enclosure.

In accordance with these objectives, this invention interposes rigid materials of different acoustic impedances in series with the conducting path of sound waves emanating from a sound propagating source, thereby achieving a reflection of the sound which reduces the volume of sound transmitted exteriorly of the sound propagating source enclosure. The phenomenon of sound transmission is a function of both density and elasticity of the sound conducting medium as shown by the formula u= /DE, where u=acoustic impedance, D=density, E=elasticity.

The features of this invention which we believe to be novel are set forth with particularity in the appended claims. Our invention itself, however, both as to its organization and use, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 represents an embodiment of our invention as applied to a stationary electrical induction apparatus; Fig. 2 is a modified embodiment of our invention as applied to a stationary electrical induction apparatus in which a plurality of rigid materials of different acoustic impedances are placed in series with the sound conduction path of the stationary electrical induction device; while Fig. 3 is an embodiment of our invention as applied to a liquid-immersed apparatus.

Referring now to Fig. 1, there is shown a transformer 1 having a magnetic core 2 and an electrical winding 3 positioned on the magnetic core. The transformer 1 is contained within an enclosure or containing tank 4 of some suitable metallic material such as steel.

Core clamps 5 extend across both side surfaces of the top and bottom of the magnetic core structure and help to maintain it rigidly in assembled relation. The magnetic core 2 is supported on its under side by one or more support members 6 which rest upon the bottom or floor of the enclosure 4. The top of the magnetic core is attached by means of one or more brace members 7 to one or more lug members 8 which are welded or otherwise rigidly attached to the inside surface of the tank 4.

The support members 6 which are positioned between the bottom of the magnetic core and the floor of the tank 4, and the brace members 7 which brace the top of the magnetic core with respect to the inside surface of the tank 4, each serve as a path by which sound propagated by the transformer or other sound propagating device is conducted from the sound propagating device to the surface of the containing tank 4.

in accordance with our invention, in order to isolate the sound propagated by the transformer core, we make the support members 6 and the brace members 7 of a rigid material having a considerably different acoustic impedance and, consequently, a different sound transmitting characteristic than that of the material of which the core and core clamps are made, and also different from the material of which the tank 4 is made. For example, if the sound propagating device, in this case a magnetic core, and the enclosing tank are made of steel, the support members 6 and the brace members 7 may be made of some material such as magnesium. The support members and brace members may also be made of material such as oil-treated fir wood, oil-treated elm wood, or dry elm wood. The support members 6 positioned between the bottom of the core and the floor or bottom of the tank 4 may be of the same material as the brace members 7 between the top of the core and the side of the tank surface, or for structural reasons, it may be desirable to have the respective materials used for support members 6 and brace members 7 different from one another.

When sound passes from the sound propagating source to the support members 6 or brace members 7 a reflection of the sound occurs, due to the difference between the acoustic impedance of the material of the magnetic core and of the support and brace members. Likewise, another reflection occurs when the sound passes from the support or brace members to the surface of the enclosing tank. If there is suificient difference between the acoustic impedances of the materials in the sound conduction path, most of the energy of the sound will be reflected back and only a relatively small proportion of the sound energy will pass through the sound conduction path to the exterior of the enclosure.

There is shown in Fig. 2 a modified form of our invention in which a plurality of materials of different acoustic impedances are placed in series with the sound conducting path between the sound propagating device and the surface of the tank-type enclosure surrounding the sound propagating device. There is shown in Fig. 2 a transformer 9 having a magnetic core 10 and an electrical winding 11 positioned on the magnetic core. The transformer 9 is positioned within a tank or enclosure 12. The magnetic coreltl is supported with respect to the bottom of the tank 12 by a plurality of'support members 13, 14, and 15 positioned in superposed relation-,with respect to one another. Thus, support member-13 is positioned in direct contact with the core clamp members 17, and itself rests upon an intermediate support member 14 which is bolted or otherwise rigidly secured to support member 13... A third support member 15 is positioned beneath support member 14 and is in direct contact with the surface of the tank floor.

, In accordance with our invention, the materials used :for the respective support members 13, 14, and 15 are so chosen that adjacent members having contacting surfaces have diiferent acoustic impedances and, consequently, different sound transmitting characteristics so that a considerable portion of the sound passing through this conduction path is reflected back upon itselt. Thus, for example, if the material of the magnetic core 16 and core clamps 17 is steel, the support member 13, which is in direct contact with the surface of the core clamp members 17, may be of some material such as magnesium, the intermediate support member 14 which is in direct contact with support member 13 may be of a material such as dry elm wood, and the bottom layer 15 which is in direct contact with the floor of the tank 12 may be a repeated layer of magnesium. Alternatively, the support 13'may be of-magnesium, intermediate support 14 may be made of steel, and the bottom support member 15 may be made of magnesium. it will be understood that the various materials which I have mentioned are by way of example only, and that various combinations of materials may be used, provided that adjacent series-connected materials in the sound transmission path are so chosen as to have widely ditierent acoustic impedances.

We have found that the greater the number of reflections of sound which occur in a given conduction path, the lower is the sound level in decibels which is transmitted to the exterior of the enclosure for the soundpropagating device. in the arrangement illustrated in Fig. 2, a first reflection is obtained when the sound passes from the steel material of the magnetic core and core clamps to support member 13 which is of a material having a considerably diiferent acoustic impedance than the core and core clamps. Similarly, when the sound passes from the material of support member 13, which is of some material such as magnesium, to intermediate a support member 14, which may beof some material such as steel, a second reflection occurs. When the sound passes from intermediate support member 14 to bottom support member 15, which is of a material having a considerably different acoustic impedance than material of support member 14, and may be, for example, another layer'of magnesium, another reflection occurs. A fourth reflection occurs when the sound passes from the bottom support member 1510 the bottom surface of the tank 12, which may be of a material such as steel. construction illustrated in Fig. 2, a total of four reflections occurs in the single sound conduction path between the bottom of the magnetic core 10 and the bottom surfaceof tank 12.

In the embodiment of our invention shown in Fig. 2, an arrangement similar to that just described for the bottom support members also occurs at the top support members connecting the top of the magnetic core to the inside surface of the side of tank 12. Thus, support member 16, which may be of some material such as magnesium, having a considerably different acoustic impedance than that of the magnetic core and core clamps, is directly connected to the core clamps 17 at the top of the magnetic core structure. Support member 16 does not extend the entire distance to the inside surface of the tank 12, but instead a connecting member 18 may be used to connect member 16 to another connecting member 19 which is rigidly attached to a lug member 2 attached to the inside surface of tank 12. Member 1% should be of some material having a considerably different acoustic impedance than members 16 and 19. Member '19 should be of a'material having'a considerably diflerent acoustic impedance than member 13 or lug '29. For example, member 16 may be of a magnesiuimmenr ber 18 may be of steel, member 19 may be of magnesium,

Thus, in the and lug 20 and tank 12 may be of steel. Thus, it can be seen that the support structure at the upper end of the transformer structure 9 of Fig. 2 comprises a plurality of rigid series-connected members, adjacent members in the series path having widely different acoustic impedances. In this manner, a plurality of sound reflections occur as sound waves pass through the seriesconnected support members.

When the sound propagating device is immersed in a liquid, the liquid serves as a transmitting medium for the sound. There is shown in Fig. 3 an embodiment of our invention applied to a liquid-immersed sound-propagating device, in this case a stationary electrical induction apparatus. There is shown a magnetic core 21 having positioned thereon an electrical winding 22. The magnetic core and winding are contained in a tank-type enclosure 23 and are immersed in an insulating liquid 24. In accordance wtih our invention, we position a barrier member 25 in the insulating liquid between the sound propagating device and the interior surface of the tank 23. Barrier 25 is preferably constructed of a plurality of layers of materials having widely diflerent sound-transmitting characteristics, just as in the case of the support members heretofore described and shown in Figs. 1 and 2. For example, the barrier 25 may comprise a layer of pressboard 26 surrounded by a plurality of hollow rings 27 of .a flexible material and containing a suitable gas, such as nitrogen. .Sound transmitted through the liquid from the magnetic core will be reflected back from the surface of the pressboard, and also the sound waves will be reflected back upon striking the gas in its flexible .containers 27. it willbe understood that we have shown the use of .pressboard, and a gas only by way of example, as materials having widely different acoustic impedances and therefore diflerent sound transmitting characteristics, and that other materials fulfilling these requirements may be used instead.

It will be seen that by interposing in the path of sound conduction various barrier members having widely diftering acoustic impedances, suincient internal reflection of the sound may be obtained to effectively isolate the sound from the exterior of the enclosure means for the sound propagating device.

While there have been shown and described particular embodiments of .our invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What we claim .as new and desire to secure by Letters Patent of the UnitedStates is:

Ina transformer apparatus comprising a metallic magnetic core enclosed within a metallic tank, said tank having a bottom portion and vertical side walls, said core spaced from said bottom portion and said side walls, supportingmeans for supporting said core on said bottom portion comprising a plurality of pieces of structurally rigid material interposed between a bottom portion of said core and said tank bottom portion, said plurality of pieces spacing said core from said tank bottom portion, said plurality of pieces being vertically superposed with respect to each other, a vertically uppermost of said vertically superposed pieces contacting said core bottom portion and a vertically lowermost of said vertically superposed pieces contacting said tank bottom portion, said vertically uppermost piece having an acoustic impedance widely different from the acoustic impedance of said core bottom portion and said vertically lowermost piece having an acoustic impedance widely diflerent from the acoustic impedance of said tank bottom portion, each of said plurality of pieces having an acoustic impedance widely different from the acoustic impedance of pieces immediately adjacent to said each piece, and means -for laterally supporting said core with respect to said side walls comprising a second plurality of superposed pieces of structurally rigid material interposed between an upper portion of said core and one of said side walls, only one of said second plurality of pieces contacting said upper core portion and only another of said second plurality of pieces contacting said one side wall, said one piece having an acoustic impedance widely difierent from the acoustic impedance of said upper core portion and said another piece having an acoustic impedance widely different from the acoustic impedance of said one side wall, each of said second plurality of pieces having an acoustic impedance widely difierent from the acoustic impedance of pieces immediately adjacent to said last-mentioned each piece.

References Cited in the file of this patent UNITED STATES PATENTS De Beaux Apr. 6, Swing et a1. Oct. 12, Miller Aug. 28, Aiken July 31, Matthews Feb. 23, Weinberger Sept. 6, Wood Mar. 9, Manual Ian. 10, Mason Apr. 11, Rockwell Feb. 26,

FOREIGN PATENTS Switzerland Ian. 17, 

